The emergence of ever growing marketing requirements and related identification needs created an increasing need for a colour parameter to be introduced in bottle packaging. This created therefore the need to provide for the possibility of producing corresponding preforms as semi-finished products for the manufacture of bottles and other containers.
A process for producing containers with two colours of different materials is known from document EP 1 559 530 A1, wherein a primary and a secondary material are injected through different injection points for both materials. This has the disadvantage that the secondary material is applied on top of the primary material, thereby generating bonding joints in the contact areas between preform subsections made of primary and secondary materials. This results in the absence of homogeneity between both materials, and also makes the process more complex. This further limits the placement options for the secondary material to precisely delimitated areas without the secondary material being diffused in the primary raw material. The second material used here is usually the same material as the base material but with a different colour, enabling the formation of a preform, resp. bottle with two different colours, but with the following restrictions. There are two separate and successive injection steps needed, whereby the colouring is made in a discrete manner, particularly in specific places and discontinuous. The method used here deposits a secondary plastic material in a pre-determined area that was a space remained empty in the original primary preform, which is a relatively weak point within the structure. It is therefore also impossible to bring an additional three-dimensional layer on top of the external wall of the preform, involving a restriction on the number of colours.
Besides, document US 2005/0252879 discloses a process for producing opaque containers with a transparent strip extending from top to bottom of the container, through which a protection from environmental light is achieved together with a possible visualization of the content. For the sake of protection, the visualization window is reduced to a limited strip, the functional width whereof should be limited to a minimum. This is a strong restriction in terms of shape, dimension and location on the container imposed by the function itself. Such a sight window is merely intended to serve as a level indicator for the food contained in the container.
Document EP 0 835 813 A1 discloses a method for producing a preform with a vertical strip in a different colour, wherein the connection line is in a recess, in order to get a straight appearance.
Document JP 03 076624 shows a similar solution, but with a co-injection, so that the transparent strip is continuous with the rest of the bottle. However, the continuity consists in a joint that is limited to the width of the container. This has the drawback to remain fragile.
Document US 2002/0058114 discloses a still further preform with multiple colours yet requiring several successive injection operations. The primary plastic material is poured into a first mould intended for the preform having its final shape in the neck region and has a very thin wall at the lower bottom part of the preform. The resulting provisional preform is then kept around the core, and said first mould is replaced by a second mould corresponding to the final form of the preform on a part that is located directly under said first area, thereby having again a very thin wall at the lower part of the preform. Subsequently, a second injection operation is proceeded. This process is further set forth analogously for a possible third or even fourth colour. The material that is visible in the lower part is thus injected around all the aforementioned thin layers. This technology is focused on injection over-moulding. A basic preform is manufactured here in one colour, after which it is transformed in a second matrix with a second colour and even still further in a third mould for a third colour, etc. . . . This method has the disadvantage that at least two steps or even three or four processing steps have to be implemented, and resp. two, three or four matrixes have to be used for each cavity. In addition, the colours can only be located in this process through the matrixes. This has further disadvantage to provide virtually no flexibility and to be also much more expensive in conception and production than with co-injection. Finally, it again offers no continuity between the different materials injected.
Document EP 1 332 861 A1 discloses a method for producing a preform with an intermediate layer being made of a recycled material. The invention discloses the solution to obtain a thinner intermediate layer in the bottom section than in the wall section, in order not to weaken the bottom section due to the use of recycled material. Neither colouring nor identification possibility is suggested here.
Document DE 43 30 451 A1 discloses a method for producing a continuous preform with two different materials, intended for implementing a high temperature resistant material for the neck section, and a cheap blow mouldable material for the wall section. Different colours allow quality control or bottle identification. But here again, the continuity consists in a joint limited to the width of the container, which remains fragile.
From WO 97/21539, there is also a known process for the manufacture of preforms or containers with various colours, which is to inject the different coloured materials sequentially and immediately one after another. The primary transparent or light coloured plastic material is injected, with a quantity determined in order to form a first part in the neck region. The dark or otherwise coloured secondary material is injected immediately after and is dosed in such a way that it fills the rest of the preform. The primary material is then injected into the pipes in order to push away the secondary material from the pipes, and at the same time to prepare for the moulding of the following preform. This approach can be applied for more than two colours. Yet in this case with two different materials, the second and third injection operation can be carried out simultaneously through a concentric valve system. As the wall of the mould and the core are relatively cold during the injection operation, a deposition of the primary material on both surfaces is obtained in the lower part of the form. The secondary material then arrives between these two deposits, with a thickness resulting in the higher part of the form which is smaller than that of the primary material. Owing to the viscosity and the pouring temperatures of both materials, a thickness can be obtained after blowing into a container which is such that the darker colour in the preform shows a more clear aspect in the container. Even a single material can be injected with selected colour pigments added directly to the injection point during a chosen part of the injection operation, thereby obtaining the desired colour at a chosen height of the preform. However, containers produced through this method have a boundary between two colours with an irregular shape, evolving as a zigzag course.
Finally, from document U.S. Pat. No. 5,595,799 a process is known for producing a preform with co-injection, involving two different coloured PET materials. Preforms with various colours at different places are obtained. The main embodiments proposed consist in preforms having dark-coloured lower half and a light or slightly coloured top half, or vice versa, or even a succession of dark/light/dark coloured preforms, respectively. This yet provides some possibilities of identification but remains limited to a single layer, and to fixed and clear areas for each colour along the wall section. The more so, the continuity consists in a joint limited to the width of the container. This remains fragile. This document yet discloses a co-injection process with two colours but remains in default to a unanimous distributed colouring over the preform and its bottle. On the contrary, the blown bottles even show very large colour variations along a horizontal plane with a wavy zigzag course between the colours, with no neat straight dividing line between the colours. Moreover, only a single colour is present at the injection point for the bottle. Again only the production of a single layer is shown in this document. Furthermore, the above process is only addressed without special colour effects mentioned, nor possibilities for adjustments, especially for the bottles.
It thus appears from the preceding that none of the above known containers or manufacturing methods is satisfactory as such.